1. Field of the Invention
This invention relates to a process for recovery of ethylene from gaseous mixture containing ethylene by absorbing ethylene with liquid absorbent.
2. Description of the Prior Art
Ethylene is one of the most important basal raw materials in the chemical industry and can be obtained by the thermal cracking of such saturated hydrocarbons as natural gas, refinery gas and petroleum fractions. Whilst, it is well known that a considerable amount of ethylene is also contained in gases derived, as a by-product, from some kinds of cracking units or gasification units, for example, in FCC off gas, ethylene plant off gas or coke oven gas. Such gases, however, usually become available in the form of a gaseous mixture containing ethylene, carbon monoxide, nitrogen, oxygen, methane, ethane, carbon dioxide, hydrogen, etc. In addition, the gaseous mixture normally contains 1,000 to 20,000 ppm of water or its vapor. Consequently, it is required to separate ethylene from the gaseous mixture to utilize ethylene for chemical industry as a raw material.
Low temperature cryogenic separation is one of the process, which can obtain a large quantity of high purity ethylene, in which the gaseous mixture is cooled to liquefy C2 plus hydrocarbons therein and then thus liquefied hydrocarbons are fractionated at a low temperature ranging from -95.degree. to -140.degree. C. However, there are drawbacks that this process requires a complicated refrigerating and heat-recovery system and also high-grade materials for the equipment which result in a high erection cost and high utility consumption because the power requirement is large. It is further reported that water and carbon dioxide contained in the gaseous mixture causes some plugging troubles in the low-temperature piping system. Therefore, the process requires a pretreating system which can reduce the contents of water and carbon dioxide to less than 1 ppm.
Another process for the recovery of ethylene from a gaseous mixture containing ethylene is composed with the application of an appropriate absorbent. In U.S. patent specification No. 3,651,159, it is described that aluminium cuprous chloride solution which chloride forms a complex with ethylene is applicable for recovery of ethylene from ethylene-containing gas. However, the reaction in which the chloride is employed should preferably be run under substantially anhydrous conditions, e.g., less than about 10 ppm water. Therefore, this process also requires a pretreating system which can reduce the content of water to less than about 10 ppm.